The present invention relates to redundant avionics in aircraft and particularly to displaying redundant instrumentation in a small aircraft.
The safety of flight in aircraft depends upon reliable operating flight instruments, such as the altimeter, attitude indicator, heading indicator, and airspeed indicator. Pilots depend upon these and other instruments to provide the information necessary for controlling the aircraft under all regimes of flight. The instruments are particularly critical during flight in restricted visibility when the pilot does not have a horizon, a view of land, or any other visual references.
Critical flight instruments are typically separate devices, but there is enough cross-correlation among the data provided by the several instruments in an aircraft so that the failure of any one instrument should not adversely affect the safety of flight. However, failure of more than one instrument under conditions of restricted visibility can and frequently has caused aircraft destruction and loss of life due to loss of aircraft control.
The instruments currently provided in aircraft are largely "low technology" and relatively primitive mechanical devices. Far better and more useful displays could be provided to the pilot by using more modern, computerized display instruments. The major advantage of current instruments is that they provide reliable information. They are, individually, simple mechanical devices with long records of reliable operation. If one instrument fails, the others provide sufficient data for successful completion of the flight.
Modern transport aircraft employ a "glass cockpit" in which the primary flight displays are electronic rather than mechanical displays. They can provide such displays because their large instrument area provides space for multiple display screens in the cockpit. These screens can be reconfigured electronically to provide critical information even if one screen completely fails.
In contrast, smaller "general aviation" aircraft, and especially single engine piston aircraft, have insufficient room for the redundant displays that make this technology practical and safe. If a single electronic screen that displays several flight-critical instruments were to fail under adverse flight conditions, the aircraft would probably become uncontrollable. Although modern electronics is reliable, it is difficult to guarantee the kind of "uptime" necessary to allow such a screen to be the sole instrument display.
The prior art shows redundant avionics systems in aircraft for fault tolerant aircraft avionics. But those systems are not selectively directed to providing a single projected display apparatus before the pilot or other operator. U.S. Pat. Nos. 4,658,359; 5,663,732 disclose systems with two separate sets of instrumentation. But this prior art does not disclose taking information from flight data sensors, and projecting it through two separate display creation apparatus at a single display screen, e.g. in a small aircraft, wherein the failure of one display creation apparatus will not interfere with operation of the other such apparatus, so that the image representative of the data collected by the sensors will still be projected on the screen even if one set of instrumentation which projects an image toward the display screen is inoperative for any reason.
Redundant instrumentation for supplying signals to redundant displays is shown in U.S. Pat. Nos. 4,845,495 and 5,297,052. The redundant control system in U.S. Pat. No. 5,739,769 also has a cockpit glass display. But none of these shows two sets of instrumentation projecting to one display screen in a manner such that the failure of one set of instrumentation still permits the other set of instrumentation to project the full image corresponding to all of the sensed data on a single display device or screen.